package smvc.animation;

/**
 * This class provides a simple callback mechanism to listeners that is
 * synchronized with all other animators in the system. There is no duration,
 * interpolation, or object value-setting with this Animator. Instead, it is
 * simply started, after which it proceeds to send out events on every animation
 * frame to its TimeListener (if set), with information about this animator, the
 * total elapsed time, and the elapsed time since the previous animation frame.
 */
public class TimeAnimator extends ValueAnimator {

    private TimeListener mListener;
    private long mPreviousTime = -1;

    @Override
    boolean animationFrame(long currentTime) {
        if (mListener != null) {
            long totalTime = currentTime - mStartTime;
            long deltaTime = (mPreviousTime < 0) ? 0
                    : (currentTime - mPreviousTime);
            mPreviousTime = currentTime;
            mListener.onTimeUpdate(this, totalTime, deltaTime);
        }
        return false;
    }

    /**
     * Sets a listener that is sent update events throughout the life of an
     * animation.
     * 
     * @param listener
     *            the listener to be set.
     */
    public void setTimeListener(TimeListener listener) {
        mListener = listener;
    }

    @Override
    void animateValue(float fraction) {
        // Noop
    }

    @Override
    void initAnimation() {
        // noop
    }

    /**
     * Implementors of this interface can set themselves as update listeners to
     * a <code>TimeAnimator</code> instance to receive callbacks on every
     * animation frame to receive the total time since the animator started and
     * the delta time since the last frame. The first time the listener is
     * called, deltaTime will be zero. The same is true for totalTime, unless
     * the animator was set to a specific
     * {@link ValueAnimator#setCurrentPlayTime(long) currentPlayTime} prior to
     * starting.
     */
    public static interface TimeListener {
        /**
         * <p>
         * Notifies listeners of the occurrence of another frame of the
         * animation, along with information about the elapsed time.
         * </p>
         * 
         * @param animation
         *            The animator sending out the notification.
         * @param totalTime
         *            The total time elapsed since the animator started, in
         *            milliseconds.
         * @param deltaTime
         *            The time elapsed since the previous frame, in
         *            milliseconds.
         */
        void onTimeUpdate(TimeAnimator animation, long totalTime, long deltaTime);

    }
}
